Stack of joined thermoplastic sheets



May 5, 1970 T. E. P'IAZZE 3,509,990

STACK OF JOINED THERMOPLASTIC SHEETS Original Filed Nov. 17, 1961 2 Sheets-Shget 1 INVENTOR FIG-8 THOMAS E. PIAZZE BY 2 29m W M $0,599

y 5, 1970 'r. E. PIAZ-ZE 3,509,990

STACK 0F JOINED THERMOPLASTIC SHEETS Original Filed Nov. 17; 1961 2 Sheets-Sheet 2 //////z/ IQ INVENTOR THOMAS E. Pl AZZE ORNEY S United States Patent 3,509,990 STACK 0F JOINED THERMOPLASTIC SHEETS Thomas E. Piazze, Mount Vernon, Ohio, assignor to Continental Can Company, Inc., New York, N.Y., a corporation of New York Original application Nov. 17, 1961, Ser. No. 153,148, now Patent No. 3,287,195, dated Nov. 22, 1966. Divided and this application Apr. 21, 1966, Ser. No. 544,232

Int. Cl. B65h 9/00; B65r 75/00 US. Cl. 206-57 9 Claims ABSTRACT OF THE DISCLOSURE This is a division of applicants copending application Ser. No. 153,148, filed on Nov. 17, 1961, now Pat. No. 3,287,195 issued Nov. 22, 1966.

This invention primarily relates to joints between a plurality of thermoplastic sheets.

Prior to the development of the present invention several ways of aligning a stack of thermoplastic bags and maintaining such bags in alignment for feed into an automatic bag filling machine, were known. One of the methods that has been used is that of aligning a stack of bags, e.g., polyethylene, and piercing the stack in the lip area with a hot needle. The bags may be pierced in one or more places as desired. This method has been found very satisfactory to maintain the stack of bags in alignment with each other; however, it has been found in practice that the hot needle method forms a chimney of weld surrounding the pierced opening. When the bags are stripped, normally one by one, from the machine, the bag material breaks away from this chimney, leaving the chimney projecting above the new bag level. This resultant chimney causes difliculty in stripping off the subsequent bags and also interferes with the operation of the gripper bar which should press down upon the lip of the uppermost bag as evenly as possible.

Another way of maintaining such stacked sheets in alignment with each other that has been previously practiced, is to fasten the sheets together with metal staples or other like fastening means. This, although being a most simple and obvious expedient has not been met with a great deal of acceptance as there is always present the danger of a staple or other fastening means finding its way into the bag, which may in many cases contain a food product.

The general object of the present invention is the provision of a temporary seal or joint between a plurality of thermoplastic sheets so that said sheets may be maintained in overlying and registered position.

Another object of the present invention is to provide a sheet jointure whereby a plurality of thermoplastic sheets disposed in overlying and aligned position may be temporarily held together in such a registered position.

A further object of the present invention is to provide a jointure whereby a thin sheet of thermoplastic material may be temporarily secured to a thicker underlying sheet of similar material.

Another object of the present invention is to provide a temporary joint between a plurality of overlying and aligned sheets of thermoplastic material wherein said joint comprises either slight mechanical interlocks or slight heat welds between the overlying sheets along sever lines thereof. v

Another object of the present invention is to provide a temporary joint between a plurality of overlying and aligned sheets of thermoplastic material wherein said joint comprises slight mechanical interlocks and slight heat welds between adjacent sheets along sever lines thereof.

Another object of the present invention is to provide a jointure of the character stated formed by a rounded edge punch element forced into and through a plurality of overlying and registered thermoplastic sheets so as to form a severed edge therethrough and thus provide mechanical interlocks and heat welds along said edge.

Another object of the present invention is to provide a jointure of the character stated wherein a thin sheet of thermoplastic material is temporarily secured to an underlying thermoplastic sheet by a rounded punch element being quickly brought down and through such sheets and forming a severed edge therethrough and temporarily securing the upper sheet to the underlying bottom sheet by means of fold-like mechanical interlocks and heat weld areas formed by the punch action along the severed edge.

Other objects and advantages of the invention will be pointed out in the following detailed description or will become apparent therefrom, said description having reference to the accompanying drawings, in which:

FIG. 1 is a pictorial view of one form of the herein included invention where a plurality (merely a few sheets have been shown for clarity) of sheets are placed upon a supporting structure and a rounded edge punch element positioned thereabove.

FIG. 2 is a side view of FIG. 1 on a reduced scale.

FIG. 3 is a side view of FIG. 1 similar to FIG. 2 but showing the punch element at its downwardmost position where it just contacts the supporting member and thus provides for the severance of the plurality of sheets.

FIG. 4 is a fragmentary transverse vertical sectional view of a modified form of the present invention wherein the supporting member has an opening defined therein and the punch element is placed in overlying and aligned relation to the opening.

FIG. 5 is a fragmentary elevational view with parts having been broken away and shown in section of another modified form of the present invention wherein a press plate having an opening therein is disposed above a plurality of sheets and above the press plate and in overlying relationship to the opening, a rounded edge hollow punch member is disposed.

FIG. 6 is also a fragmentary elevational view with parts broken away and shown in section of the modified form of the invention shown in FIG. 5 wherein the press member is shown in intimate contact with the plurality of sheets and the overlying punch element has reached its most downward position.

FIG. 7 is a plan view of the plurality of sheets depicted by FIG. 6 and the opening formed therein.

FIG. 8 is a partial vertical sectional view on an enlarged scale and taken along the line 88 of FIG. 7.

FIG. 9 is a vertical sectional view on an enlarged scale of a modified form of the invention shown in FIG. 5 showing a hollow punch withdrawn from the plurality of thermoplastic sheets after it has been utilized to sever the sheets so as to produce an opening therein.

FIG. 10 is a horizontal sectional view on an extremely large scale and taken along line 1010 of FIG. 9 and shows both the heat welds and the mechanical interlocks thereof.

FIG. 11 is a partial vertical sectional view of another modified form of the present invention wherein a thin thermoplastic sheet may be temporarily secured to a thicker underlying thermoplastic sheet, the rounded punch element being shown at its initial point of contact with the overlying sheet.

FIG. 12 is a fragmentary transverse vertical sectional view of another modified form of the present invention similar to FIG. 4 wherein the punch element is of a lesser cross-sectional area than the support defined opening and wherein a press plate having an opening therein engages the stack of sheets.

Referring to the drawings with particular reference to FIGS. 1 through 3 thereof, a stack of thermoplastic sheets or bags is placed upon supporting structure 1 which may be composed of a hard plastic, metal or any other material which exhibits the properties of being relatively inflexible and wear-resistant. The stack, generally designated 2, is comprised of a plurality of sheets or bags (as many as 200 double-sheeted bags has met with operational success) and is placed upon support member 1 in the desired aligned position. A punch element 3 having a rounded and smooth lower end 4 is rapidly brought down against and through the stack 2 so as to kiss the upper surface of the underlying support member 1 and to sever the overlying sheets including the lowermost sheet or bag of the stack. The downward movement of the punch may be controlled by known means such as stops and may be actuated by known fast-acting mechanisms such as cam movements. As the punch passes through the sheet stack, the material about the periphery of the punch is stretched thin by the extrusion forces acting thereon. The thus produced thin peripheral edges of the severed sheets are forced downwardly by the wiping action of the punch 3 thereupon and are severely worked to produce an almost instantaneous increase in temperature in the thinned out plastic edges. This instantaneous increase in temperature has been found to be sufficient to form slight heat welds between the overlying sheets proximal to their severed edges. This is, of course, possible through the thermoplastic nature of the material being worked upon. At the same time that these heat weld areas are being produced, fold-like mechanical interlocks are also being formed between the overlying sheets by the action of the downwardly moving punch 3 forcing the extruded thin edges of the individual sheets upon those underlying them. The thinned out edges of the individual sheets or films are, upon the action of the downwardly moving punch 3, bent downwardly over each other and form nested flanges about the opening produced in the sheet stack. It is this combination of mechanical interlocks and heat welds that forms the temporary securing joints between the overlying individual sheets in an aligned sheet stack: The thus formed joints retain the sheet stack 2 in superposed relationship and prevent skewing or misalignment of an individual sheet or sheets from the remainder of the sheet stack 2. Of course, it is obvious that if several holes are formedwithin a sheet stack or if an entire edge or great portion thereof is severed according to the instant invention, more assurance of keeping the sheet stack 2 in proper alignment is obtained.

As evidenced from the above description, the herein described novel method and joint produced therefrom provide a simple Way of holding a stack of sheets in aligned position by the slight mechanical interlocks and slight heat welds formed about the severed edge of said stack. Since the welded portions are slight or in other words in limited areas and only extend a short distance away from the severed edge, being for the main part in the thinned or extruded edges thereof, an individual sheet or bag may be easily removed or stripped from the remaining stack without exhibiting any tendency to tear. Also, because of the placement and extent of such welds, no objectionable chimney of fused or welded material as in the hot needle method or needle produced jointure is present. It has been found in'some cases that either the mechanical interlocks or the heat welds, themselves,

support member 5 and that both the contacting edges 8 of the punch 7 and the opening defining edges 9 of the support member 5 are rounded. Upon the downward movement of the punch 7 the overlying sheets are extruded thin adjacent the periphery of the punch and are forced downwardly upon each other to form a nested and flanged relationship with each other. In particular with the instant embodiment the portions of these stacked sheets underlying the punch will be forced into the opening 6 defined by the supporting member 5. It should be also noted that the extent of the downward travel of the punch member 7 is just enough to kiss the rounded support member edges 9 and to completely sever the overlying sheets including the bottommost sheet of the stack 2. In this embodiment, as in the previously disclosed embodiment (FIGS. 1 through 3), essentially the same slight mechanical interlocks and slight heat welds are formed Within the severed edge portions of the individual sheets. It should be also noted that the particular shape of the punch 7 is not critical and that it may take many forms, so long as the working edges thereof are smooth and rounded as opposed to a conventional cutting edge.

In another embodiment as shown in FIGS. 5 through 7, a hollow punch 10 with rounded working edges 11 is quickly passed through a stack 2 of overlying sheets supported upon the member 1 so that the working edges 11 just barely kiss the supporting member 1 and cleanly sever the overlying sheets including the bottommost sheet. A'pressure applying member 12 having a punch guiding opening 13 therein may be provided to assure most efficient results and to reduce the care involved in the above punching operation. The punch 10 may be of different forms such as star-shape, rectangular, elliptical, round, etc. as desired; the particular overall shape being no part of the invention. The downwardly moving punch 10 severs the thus thinly extruded edge portions of the sheets that surround the area worked upon by the punch, thus forming the overlying flange and nested arrangement previously referred to and specifically shown in FIG. 8. The instantaneous high heat developed at the extremely thin severed edge portions will produce the slight heat welds between the overlying sheets, and the action of the downwardly moving punch provides the slight mechanical interlocks.

The nature of the mechanical interlocks and the heat welds may be found in more detail by reference to FIGS. 9 and 10, wherein the slight mechanical interlocks (one only having been shown for clarity) are generally designated 14 and the heat welds as 15. While the showings of FIGS. 9 and 10 have special relation to the modified punch form of FIGS. 5 through 7, the basics of all the herein disclosed embodiments are essentially the same and valid explanation of all the embodiments may be had from reference to FIGS. 8, 9 and 10. The severed vertically sectioned portion of FIG. 9 has separate verticallylongitudinally disposed and transversely spaced lines and Xs marked thereon within the space between the horizontal lines within the punch formed opening which designate respectively the mechanical fold-like interlocks and the heat welds or heat weld areas. It is believed that the nature of the mechanical interlocks is adequately clear from a perusal of FIG. 10, noting the position of the section line wherefrom this figure has been taken. An interlock of a similar nature is evidenced when one takes two overlying sheets of paper (two being taken in the emphasis of clarity as has been done in FIG. 10) and moves one double portion downwardly and to the right of a midpoint while moving a second double portion spaced and in line with the first double portion upwardly and to the left of said mid-point or relatively as viewed in said FIG. 10, and thereupon squeezing the now four sheet thickness at said mid-point together.

As illustrated by reference numeral 17 in FIG. 7, slight folds or puckers will be present along the flat surface of the sheets as viewed perpendicular to their fiat surfaces, such puckers normally emanating from the points of slight mechanical interlock. This visual phenomenon is usually present, but need not be, as the mechanical interlocks can be present with-out the presence of such puckers, especially when the temporary joint along the severed edge is formed in straight line fashion as opposed to circular or multiangle severances.

When the punch is of the female type, that is, having a hollow portion defined by surrounding edge portions, it will be noted as shown in detail in FIG. 9 that the plastic material 2a bounded by the severed edges will be forced up into the punch cavity upon its downward stroke and thus upon the upward movement of the punch be carried away therein. Naturally, either upon each upward stroke or prior to the forcing downward stroke, the severed material 2a carried upward in the punch cavity should be removed therefrom. Sometimes, of course, several cycles may be completed without removal of the severed material; that is, upon each subsequent stroke the severed waste material is forced further and further up into the hollow punch cavity. Conventional means (not shown), such as compressed air or other fluid means, as well as mechanical means, may be provided for removing the severed material 2a.

In the modification shown in FIG. 11, means is provided whereby an underlying thermoplastic sheet 18 may be temporarily connected by mechanical and heat-weld means to an overlying sheet 19 of thermoplastic material. This modification may be practiced in accordance with the previously mentioned inventive concepts and it Wlll be understood that upon the downward movement of the punch element 20, which has rounded edges 21, the top sheet 19 will be immediately extruded downwardly to form a very thin severed edge thereof, and that upon further downward movement of the punch element towards its underlying support member 22 that the underlying thermoplastic sheet 18 will also be extruded thin at its severed edges upon the completed downward movement of the rounded punch 20. That is, when the punch 20 strikes or kisses the support 22, the sheets 18 and 19 will become temporarily secured together by the presence of the slight mechanical fold-like interlocks and heat weld areas present in the previously explained embodiments of the present invention. This present modification (FIG. 11) has particular utility in forming material retaining or protective covers on containers and the like and, therefore, the underlying sheet 18 may be shaped so as to present a body portion 23 having a peripheral flange 24. The sheet 18 may also be conveniently of a greater thickness than the sheet 19.

Still another modification of the present invention 18 shown in FIG. 12, wherein a plurality of stacked and aligned sheets are held under compression while being punched by a compression applying member 24 which is similar to the member 12 described in conjunction with the embodiment shown in FIGS. and 6. The stack 2 of sheets is placed upon a supporting member 25 having an opening 26 therein. A punch 27 is positioned so as to overlie the opening 26 formed within the support member and so as to pass through the punch guide opening 28 formed within pressure applying member 24. It should be noted that the cross-sectional area of the punch 27 is slightly less than that of the opening 26 formed within the support member and that both the edges 29 of the punch 27 and the edges 30 of the support member 25 are generously rounded. The operation of this modified structure functions in a manner similar to the modifications previously explained. The downward movement of the punch 27 through the opening 28 into contact with stacked sheets forces portions of the underlying stacked sheets into the opening 26. The stacked sheets are held under compression by the member 24. This downward movement of the punch 27 causes overlying sheets to be extruded thin adjacent the periphery of the punch and forces the sheets downwardly upon each other to form the previously referred to nested and flanged arrangement. The punch, upon passing into the opening 26 severs the overlying sheets through the coaction of rounded edges 29 and 30. A pressure applying member similar to 24 can, of course, be similarly utilized in operation with the previously described modification shown in FIG. 4.

From the foregoing, it should be apparent that the fold or fold-like interlock shown in FIG. 10, for example, is in horizontal section taken across one of the generally perpendicular lines indicated within the punch hole in the stack 2. It should be considered that the section line 10-10 is passing through said line but that the section line is shown clear of said line in order to avoid confusion. It is to be understood that the hollow plunger in passage through the pack results in the drawing of the edges of the stacked films or sheets defining the holes out of plane and downward, thinning the film margins and extending the hole defining perimeter thereof. It will be apparent that this thinning of the film or sheet margins brings about an increasing of marginal area, and this increasing of marginal film areas must be forced into the same OD of the punch opening, and thus vertical folds and interlocks 14 result as in the showing in FIG. 10, there being weld areas 15 provided between each two adjacent interlock-s 14, as indicated between Xs in FIG. 9. When the punch 10 is forced through the stack of sheets forming the interlocks by the thinning and enlarging of the marginal areas and the weld areas 15 resulting from the heat developed in the punching action, and then is withdrawn, it leaves an opening which in this particular illustartion is cylindrical in form. The wall defining this cylindrical cavity is composed of compressed edges of the sheets which are fused in spots and interlocked, in other spots as shown at 14 and 15 in FIG. 10. The channel or cavity or what appears to be an open space at the center of FIG. 10 corresponds to the folds, wrinkles or distortions indicated at 17 in FIG. 7.

It will be readily apparent that when a number of sheets of film are laid one upon another, the height of the stack is greater than the total of the thicknesses of the individual sheets, unless pressure is applied to eliminate the layers of air that naturally occur between the sheets. Accordingly, when punch pressure is applied to a limited area of such a stack of sheets, a local compression occurs and the area of the film in the vicinity of the punch is increased as the film elongates in the manner above stated. However, since the actual area of film being elongated or stretched is greater than the area actually covered by the punch, fold-over, wrinkles and creases in that adjacent area naturally occur and provide the mechanical interlocks herein described and schematically illustrated in FIG. 10. When this wrinkling or creasing takes place it causes one sheet to interlock with either one other sheet or several other sheets, the number being dependent on gauges of the sheets and the height of the original stack, among other factors.

Film or sheet material of the thermoplastic type that may be heat-sealed may be utilized in the herein disclosed invention Mylar (polyethylene terephthalate), Saran (v-inylidene chloride-vinyl chloride copolymer) and both high and low density polyethylene are specific examples of polymeric sheet materials that have met with particular success.

It will become obvious from a reading of the above description of the present invention that the advantages of the prior art methods are maintained, but not at the 7 expense of their disadvantages. It can be seen that the herein described method and the temporary joint pro duced thereby, provides an easy, simple and inexpensive way of maintaining a stack of thermoplastic sheets together and in aligned position. This invention has particular utility in bag dispensing devices, but is not limited thereto.

I claim:

1. A plurality of separate superimposed thermoplastic sheets joined together along an edge thereof by portions of said sheets folded upon themselves to form spaced mechanical interlocks lying at least in part generally perpendicular to the plane of the sheets, and heat weld areas disposed intermediately of said spaced mechanical interlocks.

2. The plurality of superposed sheets of clairnl wherein a temporary joint is formed to maintain said sheets in said superposed condition for use in an automatic bag-feeding machine and said mechanical interlocks and heat weld areas are proximal to a severed edge of said sheets.

3. The plurality of superposed sheets of claim 1 wherein said interlocks and heat weld areas are disposed at the severed edges of a hole passing through the stack of superposed sheets.

4. The plurality of superposed sheets of claim 3 wherein said hole is circular and is positioned inwardly of those edges of said sheets which describe the sheet boundary edges.

5. The plurality of sheets of claim 1 wherein said sheets are temporarily joined in aligned position by said interlocks and heatweld ,areas between said. overlying sheets and wherein said interlocks and heat weld areas are proximal to a severed edge portion of said sheets.

6. The plurality of sheets of claim 1 wherein said mechanical interlocks and heat weld areas form a'joint between the superposed sheets; said mechanical interlocks comprising interfolded portions of said sheets.

7. The plurality of thermoplastic sheets of claim 6 wherein said heat weld areas are between said interlocked portions.

8. The plurality of sheets of claim 1 wherein said interlocks are between at least adjacent ones of said stacked sheets.

9. The plurality of sheets of claim 1 wherein said interlocks are formed in the surface of a cylindrical hole; the cylindrical hole being formed through the stack of sheets substantially perpendicular to the plane of each of said sheets.

References Cited UNITED STATES PATENTS 2,325,673 8/1943 Gurwick 161--104 X 3,021,947 2/ 1962 Sylvester et a1. 206-57 3,168,424 2/1965 Sendor 156-250 X ROBERT F. BURNETT, Primary Examiner R. O. LINKER, JR., Assistant Examiner Us. 01. X.R. 

